This invention relates to the interlocking of mechanical components and, more particularly, to the interlocking of a male cylindrical component and a female cylindrical component to allow cylindrical rotation therebetween, with or without relative axial movement.
A number of types of mechanical devices include components that translate relative to each other while maintaining a precisely defined, axially aligned relationship. In an example of interest, an optical zoom lens requires that tubular housings containing the optical elements rotate relative to each other about, and simultaneously translate parallel to, a central optical axis to change the spacings of the optical elements. In other applications, the two tubular housings rotate about the optical axis but do not translate relative to each other along the optical axis. In each case, the housings rotate about the optical axis, but must remain well-aligned along the optical axis so that the optical signal is not distorted.
In such devices, the two components are interlocked together in a manner that produces and allows the required relative mechanical movement. The interlocking element may be, for example, a thread or a projection on one cylindrical component that is received in a helical groove on the other cylindrical component. In another approach, such as that described in U.S. Pat. No. 6,288,855, a spring component locks the two cylindrical components together in a manner that allows the required relative movement while producing a preload that prevents play between the cylindrical components and backlash when the direction of relative rotational movement is reversed.
The approach of the ""855 patent provides a substantial improvement over the thread or projection interlock. In the work leading to the present approach, the inventor has recognized that in any of these interlock structures problems remain for some applications. The interlock structures require the use of a flowable lubricant such as an oil or grease between the two components so that they move smoothly relative to each other. The lubricant may be messy to work with, and may inadvertently produce contamination of the elements of the mechanical structure, as for example by producing a coating on lenses that interferes with their optical performance. The lubricant may degrade over time in service. For mechanical devices that are used in a vacuum, the lubricant may outgas.
Consequently, there is a need for an approach that achieves the preloading advantages of the ""855 patent but does not require the use of flowable lubricants between cylindrical components. The present invention fulfills this need, and further provides related advantages.
The present invention provides a structure and a method for its preparation. The structure includes two cylindrical components that fit together, one inside the other. A locking arrangement permits the two components to rotate cylindrically relative to each other and also to move axially with respect to each other as needed. The two cylindrical components are preloaded, so that there is no play between the cylindrical components or backlash upon reversing the relative movement of the cylindrical components. The preload and avoidance of play and backlash are achieved over a wide temperature range without binding of the cylindrical components. This approach may be used with very thin-walled cylindrical components. The locking arrangement may be made to preload the cylindrical components in the axial direction. No flowable lubricant is used between the cylindrical components, yet the starting friction and continuing-movement friction between the cylindrical components is small. The locking arrangement is inexpensive to fabricate and does not require any precision parts or machining.
In accordance with the invention, a mechanical device comprises a female component having a right-circular cylindrical internal surface and a cylindrical axis, and a first helical recess in the internal surface of the female component. A male component has a right-circular cylindrical external surface sized to be slidably received within the right-circular cylindrical internal surface of the female component, with a second helical recess in the external surface of the male component. The second helical recess has a helical pitch which is the same as that of the first helical recess, so that the second helical recess is in facing relationship along its length to the first helical recess when the male component is assembled to the female component. A retainer is received within the first helical recess and the facing second helical recess when the male component is assembled to the female component. The retainer has an organic plastic retainer outer surface. The organic plastic retainer outer surface is preferably polytetrafluoroethylene, commercially available as Teflon(trademark) polymer.
The helical pitch of the two helical recesses may be zero, in which case the two components rotate relative to each other but do not axially translate relative to each other. The helical pitch of the two helical recesses may be greater than zero, in which case the two components rotate relative to each other and axially translate relative to each other.
In a preferred application, at least one of the female component and the male component supports an optical lens. In any application, the cylindrical components may be made of the same materials or different materials. For example, the female component may be made of a female-component plastic, and the male component may be made of a male-component metal.
The retainer may be of any operable physical form. In one embodiment, the retainer is a solid piece of a retainer material having the organic plastic retainer outer surface. In another embodiment, the retainer is an annular piece of a retainer material having the organic plastic retainer outer surface. The central cavity of the annular retainer may be a metallic filler wire, such as a solid filler wire or, more preferably, a multistrand filler wire.
Desirably, the female component has an internal-surface cylindrical diameter of the internal surface that is greater than an external-surface cylindrical diameter of the external surface of the male component by a clearance of from about 0.03 to about 0.05 millimeters. The first helical recess may have a shape of a first groove having converging sides, and the second helical recess may have a shape of a second groove having converging sides. There may be a stop limiting the extent of rotation of the male component with respect to the female component. It is preferred that there be no flowable lubricant between the female component and the male component.
Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. The scope of the invention is not, however, limited to this preferred embodiment.